// Video Post Type ID, Retrieve the post ID within the query loop
$post_id = get_the_ID();

$source = streamtube_core()->get()->post->get_source( $post_id );

// OR $source = get_post_meta( $post_id, 'video_url', true );

if( wp_attachment_is( 'video', $source ) ){
    // Source is a video attachment
    // Get playable url
    $source_url = wp_get_attachment_url( $source );
}else{
    // Otherwise, source is an URL or embed/script code.
}